Impacts and Functioning of In-Stream Structures

Channel responses were documented over a decade for a relocated stream channel in central Pennsylvania. The case study illustrates channel responses when a “natural channel design” incorporated hard points to reduce uncertainties and hold the channel in place. In particular, the study focused on the effect of the hardpoints had on channel development. Current conditions were compared with those from a survey taken 10 years prior, as well as the results from a sediment transport model that had been used to predict changes over a 50-year period. The survey measurements were used to assess the ability of the model to predict those changes. In-stream structures include rock vanes at the head and tail of riffles, root wads and rock linings at the outside of meander bends, and J-hooks used to reduce near bank velocity. Results show that the model did a good job of predicting the changes in the channel provided that the in-stream structures remained in place.